1. Field of the Invention
The present invention relates to a large transport ship such as a tanker, and relates particularly to a large transport ship which does not require ballast.
2. Description of the Background Art
In conventional large transport ships such as tankers, bulk carriers, container ships, LNG carriers and car carriers, a construction is used wherein ballast is loaded onto the ship in order to prevent problems associated with a shallow draft in the case of an empty load, and in order to control the center of gravity.
In other words, if the draft is shallow, problems occur in that; (1) the degree of hogging during navigation is large, and the shearing force and longitudinal bending moment applied to the hull are also large, (2) during navigation, the ship is exposed to the impact of waves striking the ship bottom (so called xe2x80x9cslammingxe2x80x9d), (3) the propeller cannot be immersed fully, and emerges from the water, which causes a decrease in the propulsion performance, and an increase in the load fluctuation on the propeller and the main engine (causing so called xe2x80x9cpropeller racingxe2x80x9d), and (4) the rudder cannot be submerged sufficiently, causing maneuverability to worsen. In order to resolve these problems, ballast is loaded onto the ship to lower the draft.
Moreover, in this type of large transport ship, in order to ensure a large freight capacity and reduce construction costs, it is standard for the ship bottom to be a flat planar shape.
Furthermore, in a ship hull for which the center of gravity tends to be high, because it is necessary to lower the center of gravity to improve the stabilizing capabilities of the hull, the center of gravity is adjusted by loading ballast into the ship bottom, and conversely, in a ship hull for which the center of gravity tends to be too low in an unloaded state, the center of gravity is adjusted by loading ballast at a high position, to raise the center of gravity of the ship. Furthermore, if the ship heels during loading, it is possible to control the balance of the ship by temporarily loading ballast as a counterweight.
As described above, by loading ballast it is possible to both resolve the above problems associated with a shallow draft, and also appropriately control the center of gravity
However, the conventional large transport ships described above suffer from the problems described below.
Namely, in general sea water is used as the ballast, but if the large transport ship takes on this sea water in a loading area, travels to another area of sea, and then dumps the sea water ballast into the sea so that cargo can be loaded at this other site, it is possible that marine species from the sea area in which the ballast was loaded can enter the sea at the other area, potentially changing the ecosystem. Ideas such as replacing the ballast while on the open sea, or sterilizing the ballast water before dumping, have been proposed as solutions to this problem, but these measures are insufficient to resolve this problem completely.
Furthermore, the amount of ballast water depends on the type of ship, but is generally approximately 30% of the displacement of the ship, meaning that the ship carries an unnecessary and unpaid load when in an unloaded state. Consequently, fuel is wasted, which is also a problem from the viewpoint of energy conservation.
In consideration of the above circumstances, an object of the present invention is to provide a large transport ship which can resolve the problems associated with changes in the draft corresponding to the state of the load, without using ballast water.
A large transport ship according to a first aspect of the present invention comprises a bow, a stern, and a ship bottom, and the shape of the ship bottom from the bow to the stern, when viewed on a cross-section perpendicular to a longitudinal direction of the ship bottom, is tapered towards a center of the ship bottom in a widthwise direction thereof
According to the large transport ship of this first aspect, by using a tapered shape for the shape of the ship bottom, the ship can be submerged deeper than a conventional ship with a flat bottom, by an amount equivalent to the reduction in volume achieved by cutting away the edges of the flat bottom.
Consequently, the variety of problems which occur when the draft is shallow (including the increase in the shearing force and longitudinal bending moment applied to the ship due to hogging, slamming, propeller racing, and poor maneuverability and the like) can be avoided.
Furthermore, according to this construction in which the shape of the ship bottom is a tapered shape, because the draft can be deepened without using the conventional ballast water, concern about the effects on an ecosystem of the dumping of ballast water can be eliminated.
In a similar manner, because it is possible to navigate in an unloaded state without loading ballast water, excess fuel is not consumed, which contributes to the move towards more energy efficient transport.
The ship bottom, when viewed in the cross section, may be a V shape formed from straight lines which extend from the center to both edges thereof
In this case, because the main section of the ship bottom is formed from two simple planar inclined faces, the construction of the ship bottom is simpler than the case in which the ship bottom is a curved surface.
Either one of a parallel section and a center section of the ship bottom, when viewed in the cross section, may display an angle between inclined faces on each side of the center within a range from 60xc2x0 to 170xc2x0.
Problems may occur if the angle between the two inclined faces on each side of the center exceeds 170xc2x0, as the draft cannot be deepened sufficiently, or if the angle is smaller than 60xc2x0, as the required displacement cannot be ensured. Consequently, an angle within the range from 60xc2x0 to 170xc2x0 is preferable.
A large transport ship according to a second aspect of the present invention comprises a bow, a stern, and a ship bottom, wherein a displacement volume from a center position in a longitudinal direction to the stern is greater than a displacement volume from the center position to the bow.
According to the large transport ship of this second aspect, the front half of the ship, from the center in a longitudinal direction to the bow, can be submerged more deeply than with conventional hulls. Consequently, it is possible to avoid the problems which occur when the draft of the front half of the ship including the bow is shallow (such as the problem of an increase in the shearing force and longitudinal bending moment applied to the ship due to hogging, and the problem of slamming). In addition, in this construction, because the draft can be deepened without using the conventional ballast water, concern about the effects on an ecosystem of the dumping of ballast water can be eliminated. In a similar manner, because it is possible to navigate in an unloaded state without loading ballast water, excess fuel is not consumed, which contributes to the move towards more energy efficient transport.
Furthermore, by ensuring that the displacement of the rear half of the ship from the center in the longitudinal direction to the stern is greater than that of the front half, it is possible to ensure approximately the same total displacement as a conventional ship.
In the first aspect, the large transport ship, a displacement volume from a center position in a longitudinal direction to the stern may be greater than a displacement volume from the center position to the bow.
In this case, the front half of the ship, from the center in a longitudinal direction to the bow, can be submerged more deeply than with conventional hulls. Consequently, it is possible to avoid the problems which occur when the draft of the front half of the ship including the bow is shallow (such as the problem of an increase in the shearing force and longitudinal bending moment applied to the ship due to hogging, and the problem of slamming). In addition, in this construction, because the draft can be deepened without using the conventional ballast water, concern about the effects on an ecosystem of the dumping of ballast water can be eliminated. In a similar manner, because it is possible to navigate in an unloaded state without loading ballast water, excess fuel is not consumed, which contributes to the move towards more energy efficient transport.
Furthermore, by ensuring that the displacement of the rear half of the ship from the center in the longitudinal direction to the stern is greater than that of the front half, it is possible to ensure approximately the same total displacement as a conventional ship.
A large transport ship according to a third aspect of the present invention comprises a bow, a stern, and a ship bottom, and the stern comprises a propulsion mechanism and an elevator which raises and lowers the propulsion mechanism in a vertical direction.
According to the large transport ship of this third aspect, when the draft is comparatively shallow when the ship is in an unloaded state, by lowering the propulsion mechanism, it is possible to fully submerge the propulsion mechanism, and thereby avoid the problem of propeller racing with greater certainty. Conversely, when the draft is comparatively deep when the ship is fully loaded, by raising the propulsion mechanism, the propulsion mechanism can be moved away from the sea floor sufficiently to allow navigation in shallow water. Furthermore, an added benefit of moving the propeller away from the hull by lowering the propulsion mechanism is that the effects of vibration on the hull caused by the propeller can be reduced.
In the first or second aspect, the stern may comprise a propulsion mechanism and an elevator which raises and lowers the propulsion mechanism in a vertical direction.
In this case, in the same manner as the third aspect, when the draft is comparatively shallow when the ship is in an unloaded state, by lowering the propulsion mechanism, it is possible to fully submerge the propulsion mechanism, and thereby avoid the problem of propeller racing with greater certainty. Conversely, when the draft is comparatively deep when the ship is fully loaded, by raising the propulsion mechanism, the propulsion mechanism can be moved away from the sea floor sufficiently to allow navigation in shallow water. Furthermore, an added benefit of moving the propeller away from the hull by lowering the propulsion mechanism is that the effects of vibration on the hull caused by the propeller can be reduced.
A large transport ship according to a fourth aspect of the present invention, either one of a ship bottom, and a ship bottom together with lower side sections of the ship, comprises a buoyancy generator which can be filled with gas.
According to the large transport ship of the fourth aspect, when the ship is in a fully loaded state, it is possible to ensure sufficient buoyancy by filling the buoyancy generator with gas, and furthermore, when the ship is in an unloaded state, by employing a construction in which sea water can flow freely through the buoyancy generator without stagnating, the buoyancy can be decreased and the draft further deepened, and furthermore, marine species are not transported to other sea areas. Consequently, it is possible to control the draft with a greater degree of flexibility according to the state of the load, for example whether the ship is fully loaded or empty, while also preventing the transportation of marine species.
In the large transport ship according to the first, second, or third aspect, either one of the ship bottom, and the ship bottom together with lower side sections of the ship, comprise a buoyancy generator which can be filled with gas.
In this case, in the same manner as the fourth aspect, when the ship is in a fully loaded state, it is possible to ensure sufficient buoyancy by filling the buoyancy generator with gas, and furthermore, when the ship is in an unloaded state, by employing a construction in which sea water can flow freely through the buoyancy generator without stagnating, the buoyancy can be decreased and the draft further deepened, and moreover, marine species are not transported to other sea areas. Consequently, it is possible to control the water level with a greater degree of flexibility according to the state of the load, for example whether the ship is fully loaded or empty, while also preventing the transportation of marine species.